2-Bromo-6-hydrazinylpyridine

The title molecule is essentially flat. In the crystal the molecules are linked by a system of N—H⋯N hydrogen bonds formed by the hydrazinyl group, a Br⋯Br halogen bond, and π-stacking between the pyridine rings.


data reports
and (I2), however. While in (I1) the hydrazine nitrogen atom N3 is in the syn-disposition with respect to the pyridine nitrogen atom N1, with N1-C5-N2-N3 = 5.4 (3) , in (I2) the hydrazine group is in the anti-conformation, with the corresponding torsion angle N4-C10-N5-N6 = 171.0 (2) . For comparison, in 3-chloropyrid-2-ylhydrazine (Wang et al., 2010), the hydrazine group is in the syn-conformation, with the respective torsion angle being À9.6 . The only other structural analogue of (I) for which X-ray diffraction data are available is 2-hydrazinopyridine; however, no crystal structure of this molecule as a free base is known. In crystalline palladium(II) (Drożdżewski et al., 2006) and copper(I) (Healy et al. 1988) complexes of 2-hydrazinopyridine, both the terminal hydrazine and pyridine nitrogen atoms are co-ordinated to the same metal ion, thus stabilizing the syn-conformation of this ligand. In the 2-hydrazinopyridine dihydrochloride salt (Zora et al., 2006), both the terminal hydrazine and pyridine nitrogen atoms are protonated and thus forced into the anti-conformation.
The conventional hydrogen bonding in the crystal structure of (I) is extensive and involves all nitrogen atoms of both hydrazine groups and pyridine rings (Table 1) and is shown in Fig. 2. The hydrogen-bonding pattern is represented by a network of infinite chains, which propagate in the [100] direction. This network features R 2 2 (7) rings, which are formed by almost coplanar molecules (I1) and (I2), as shown in Fig. 1, and which represent the shortest intermolecular heteroatom contacts in the crystal. A centrepiece of the network is N3, which participates in five short heteroatom contacts, once as an acceptor and four times as a donor of hydrogen bonds [two bifurcated N-HÁ Á Á(N,N) links]. Over half the hydrogenbonding contacts are multicentered and include two bifurcated hydrogen bonds for donor atoms H3A and H3B, and N6 acts as a double acceptor ( Fig. 2; Table 1).

Figure 1
Atomic numbering and displacement ellipsoids at the 50% probability level for molecules (I1) and (I2). Hydrogen bonds are shown as dashed lines.

Figure 2
Molecular packing of (I). Hydrogen bonds are shown as cyan dotted lines. Crystallographic axes colour codes: a -red; b -green; c -blue.
rings of both (I1) and (I2) are involved in a well-defined system of staggeredstacking interactions (Table 3). These various interactions can be seen in the Hirshfeld surface of the title compound (Fig. 3).

Synthesis and crystallization
The title compound was prepared following an established synthetic route (Zoppellaro et al., 2004). Specifically, 8.0 g (34 mmoles) of 2,6-dibromopyridine, 15 ml (310 mmoles) of hydrazine hydrate, and 2 ml of 1-propanol were heated at 80 C for 12 h. The reaction mixture slowly separated into two layers, with the lower layer taking about 5 ml, then the mixture homogenized back. After cooling overnight at 4 C, the solution deposited pale-yellow needles of the title compound suitable for further X-ray diffraction studies.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. Enantiopurity of the crystal chosen for data collection was established on the basis of the Flack absolute structure parameter determined [0.012 (5) for 999 quotients (Parsons et al., 2013)].

Funding information
Funding for this research was provided by: National Institute of Food and Agriculture (grant No. Hatch 1023929 to T. P. Mawhinney); University of Missouri, Experiment Station Chemical Laboratories.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

data-2
IUCrData (2023). 8, x230169 Refinement. The hydrazine H atoms were treated by a mixture of independent and constrained refinement while the methine hydrogen atoms were initially placed in calculated positions. All hydrogen-atom coordinates were allowed to refine freely, while displacement parameters were constrained to ride on the carrier atoms [U iso (methine H) = 1.2U eq ].